In subsea production, electrically operated apparatuses below sea level are typically supplied by power from sea- or land-based host facilities. The power is provided from the external sources to the subsea devices via cable conductors to submerged process control equipment, pumps and compressors, transformers, motors, and other electrically operated equipment. As these components are disposed subsea and are typically enclosed and protected by water-proof pressure vessels, power is provided by means of a cable termination and connector, which may be an electrical penetrator, designed to penetrate and provide power through a bulkhead.
In existing penetrator assemblies, the conductor pin of the penetrator is embedded in an insulator body, which may be seated in a penetrator housing and is sealed against the penetrator housing by means of O-rings, or other types of seals. In submerged applications the electrical penetrator must be protected from the ingress of water. Integrity of the seal is critical to operation of the subsea equipment and it is important to avoid use of materials prone to degradation and failure over time due to harsh conditions. At operational water depths down to and below 1,000 meters the penetrator and subsea device are both subjected to immense external pressure. This pressure requires a penetrator structure that is adapted to operate despite high external pressures and differential pressures over seals.
In one application an electrical penetrator may be used to power subsea electric submersible pump (ESP) equipment and the like which pump hydrocarbons in oil well installations, and also in other applications such as high pressure downhole electrical penetrations and other penetrations to provide power to various types of subsea equipment. The penetrator extends through the wall or bulkhead of the vessel in which the equipment is located, and is normally connected to power cables at one end for connecting the equipment to an external power source. In an ESP application, the connection or penetrator cannot be isolated from the pumping pressure for practical reasons. This creates an extreme environment for the connector or penetrator in terms of pressure, temperature, and high voltage. The penetrator must transfer power to the motor as well as maintaining a pressure barrier for both internal pressure created by the ESP and external pressure caused by the depth in seawater. The temperatures are increased due to fluid temperatures as well as resistive heating of the electrical elements. These penetrators must also be able to resist sustained intense heat from a hydrocarbon fire and maintain both electrical connectivity and seal integrity in high temperature and material stress situations.
In a typical electrical penetrator or feed-through component a set of seals and/or O-rings are used to prevent the ingress of external fluids into the subsea device and to prevent internal fluids from escaping. The seals must be qualified to show that they meet certain standards such as those set by the American Petroleum Institute (“API”) for subsea oil and gas applications. Such standards may include API 6A and API 17D. Seals used with electrical penetrators may also be qualified to prove that they pass extended pressure and heat cycles, and “make or break” testing cycles where alternating pressures are applied to the seals. These qualification measures are expensive and time consuming. It may be difficult to find or design a seal suitable for a particular electrical penetrator. Existing systems, apparatuses, and methods for electrical penetrators and penetrator assemblies are known and are described in at least U.S. Pat. No. 8,287,295, entitled ELECTRICAL PENETRATOR ASSEMBLY (Sivik et al.), and U.S. Pat. No. 8,968,018, entitled ELECTRICAL PENETRATOR ASSEMBLY (Sivik et al.), each of which are incorporated by reference herein in their entirety.
Furthermore, seals such as those described above may need to be replaced or may fail. Problems also exist with the installation and replacement of these seals and O-rings. The seals or O-rings may become damaged, dislodged, or may shift in the seal housings. Any of these issues may cause a leak or seal failure, resulting in damaged equipment, production downtime, and lengthy and expensive repair and replacement procedures. To overcome these problems electrical penetrators and sealing mechanisms not requiring O-ring seals were developed and are described in U.S. patent application Ser. No. 14/980,106, entitled RADIALLY AND AXIALLY-COMPRESSED CERAMIC SEALING METHOD AND APPARATUS, by Spahi et al., filed Dec. 28, 2015, which is incorporated by reference herein in its entirety. However, the system and method disclosed therein may susceptible to strain issues and the ceramic penetrator may crack or otherwise fail from strain on the penetrator from the shell or housing.
For example, the ceramic penetrator described therein may be subjected to concentrated bearing stresses or shearing stresses that may cause the ceramic components of the ceramic penetrator to crack or fracture. These stresses may be present when the ceramic penetrator is installed in a bulkhead penetrator assembly, when connectors (e.g., plugs or sockets) are connected to one end of the ceramic penetrator, when subsea currents or other subsea forces exert pressure on the subsea equipment, or when other subsea assemblies attached or otherwise connected to the bulkhead penetrator assembly in which the ceramic penetrator is disposed are moved or otherwise shift. Cracks or fractures or other damage to the ceramic penetrator at high pressures may compromise seal integrity can may lead to equipment failure or other more catastrophic failures.
What is needed is a stress reduction apparatus and related method of providing strain relief or for reducing stress on a ceramic electrical penetrator in a shell or housing.